As an example, optical devices are commonly used by military or law enforcement personnel for conducting operations in low light or night conditions. Optical devices may include one or more image sources for providing an enhanced image to the user. Such an enhanced image may be provided by a fused optical goggle system.
Brightness tracking is an important feature of a fused optical system. By monitoring the brightness of the scene content of an image intensification (I2) tube, for example, by means of an output voltage proportional to the screen current, the brightness of an optically-fused display may be automatically adjusted so as to match the image intensification tube output. The brightness tracking is important to the performance of the optically-fused goggle, because it prevents either the display or the I2 tube from overwhelming the eye of the viewer. Not all image intensification tubes, however, provide an electrical signal output that is proportional to the scene content brightness of the tube.
There exists a need, therefore, to capture an entire scene content of an image and provide a direct measurement of the brightness of the image; and use the brightness of the image to provide a means for controlling the brightness of another image viewing the same scene content. There is also a need to measure brightness of an image without adding a built-in proportional electrical output (such as a screen current monitor) that measures such brightness.